The present invention relates to a throttle valve control device for controlling an intake air flow rate in an internal combustion engine in response to engine operating conditions, and more particularly, to so-called a limp-home mode drive mechanism upon failure of a motor-driven throttle valve control device.
In a motor-driven throttle valve control device in which a throttle valve is driven with a DC motor or a stepping motor etc. (hereinbelow, referred to as a motor), it is necessary to have a fail-safe function to, even when a control circuit or the motor is broken, keep a throttle valve opening capable of performing a vehicle limp-home travel for e.g. moving the vehicle to a safe place.
Further, for prevention of so-called throttle valve lock state (sticking state), where the throttle valve can not be opened with a motor torque any more upon engine starting and which is caused by for example throttle valve freezing or adhering of a viscous substance on an intake passage wall surface, a fail-safe function to keep the predetermined throttle valve opening position more than a full-closed position upon engine key off time (in other words, when the electric motor-driven actuator is not energized) is required. The opening for realizing such limp-home function and valve lock (stick) prevention function are called as e.g. an limp-home opening, an initial opening or a default opening. This technique is disclosed in Japanese Published Unexamined Patent Application No. 2002-256894.
In the above-described conventional motor-driven throttle valve control device, one spring member, in which a first spring served as a default spring and a second spring served as a return spring are integrally formed by a length of spring wire, is used for the device. Further a hook is formed between the first spring and the second spring. In an opening direction of the throttle valve, a force of the first spring exerts on a throttle shaft until the hook of the spring member comes into contact with a default stopper of a throttle body. In a closing direction of the throttle valve, a force of the second spring acts on the throttle shaft until both side surfaces of the opener member are held with the hook of the spring member and the other end. In this arrangement, limp-home mode when current supply for the actuator is stopped due to some factor is achieved by one opener member and one spring member.
However, in this arrangement, as the two members (return spring and default spring) constituting one spring are serially arranged in an axial direction, the axial length is prolonged.